1. Field of the Invention
This invention relates to an improved method for quenching metal parts and, in particular, to a method for providing a uniform distribution of quenching medium around the part being quenched.
2. Background and Prior Art
The quenching of metal products, due to its great effect on the mechanical properties of the metal part being quenched, is one of the most critical steps in heat treating. The cooling rates during quenching determine temperature and stress distribution, phase transformations, microstructure, and deformation as well as residual stresses after quenching. The quenching of small metal parts or parts of simple geometry may be conveniently accomplished by immersion. However, the quenching of parts having a complex geometry or elongated metal parts, such as pipes, rods, tubes, bars, and the like, is more difficult and has been the subject of numerous developments over the last century. Attempts have been made to improve the manner in which such parts are quenched and to provide better control over distortion and cracking.
One of the more efficient methods for achieving low distortion and cracking during quenching is that of spray quenching. Various quenchants have been used for this purpose. Compared to other types of quenchants, such as oils, polymeric solutions, inert gases, etc., water is advantageous in that it is generally less expensive, readily available, and environmentally acceptable. However, water, like other evaporative quenchants, often produces a non-uniform quench, which may result in spotty hardness, distortion or cracking. The non-uniformity is mainly the result of a relatively unstable vapor blanket formed on the metal being quenched. It has been found that the use of a uniform and powerful spray system helps in reducing the non-uniformity problem caused by the vapor blanket formation. However, spraying alone, does not normally help in getting the metal part covered uniformly. Using current technology, the necessary level of uniformity may be achieved by rotating the part while being quenched. The rotational speed is normally dependent on the longitudinal feed of the part. Although this technique can efficiently complement the spraying effect and give good results for a wide range of applications, it has a significant disadvantage that sometimes limits its usefulness. The rotational speed of the metal part is limited to a certain maximum value due to its dependence on the longitudinal feed. The longitudinal feed is also limited by other process parameters, such as part size and geometry. This restricted rotational speed becomes the limiting factor for achieving high levels of uniformity and consequently high levels of quality.
Quenching apparatus described in the prior art includes a variety of devices for spraying quenching heat treated metal pipes, tubes, etc. U.S. Pat. No. 3,507,712 to Scott discloses a pipe-quenching apparatus wherein water spray from spray nozzles mounted on a manifold ring are directed to the pipe as the pipe travels lengthwise.
U.S. Pat. No. 3,675,908 to Amend discloses a pipe-quenching apparatus wherein quenching fluid is sprayed in a cone shaped spray against a longitudinally moving pipe as the pipe enters a sleeve wherein the quenching fluid richochets between the pipe and the inner surface of the sleeve to increase the quenching effect.
U.S. Pat. No. 4,305,574 to Amend discloses a pipe-quenching device wherein a high velocity spray of quenching fluid is directed to a longitudinally moving pipe at an acute angle to the direction of travel of the pipe.
U.S. Pat. No. 4,444,556 to Andersson discloses a cooling apparatus wherein an axially moving hot metal tube passes through a cylindrical cluster of individually repositionable spray nozzles.
It is an object of the present invention to provide an improved system for the quenching of elongated metal workpieces, such as pipes, bars, rods, tubes or the like.
It is a further object to provide a method and apparatus for quenching of elongated metal workpieces wherein the workpieces are moved axially through spinning spray quench headers.
It is a further object to provide a method and apparatus for the spray quenching of metal workpieces that will allow a more uniform distribution of quenching liquid around the metal workpiece than has been possible with the spray quenching methods of the prior art.
The above and other objects are achieved in accordance with the present invention which comprises a method and apparatus for quenching metal workpieces wherein a metal workpiece to be quenched is moved longitudinally through at least one rotating spray unit having a plurality of fluid outlets distributed over an inner surface thereof through which sprays of quenching fluid are directed at the metal workpiece. For most quenching operations it is preferred that the outlets through which the sprays of quenching fluid are directed are distributed in a substantially even pattern over the inner surface of the spray unit.
The present apparatus may be used in the spray quenching of workpieces of various sizes and shapes. Small workpieces of complex geometry, such as, gears or the like, may be quenched by placing in an open weave container, such as a basket and transporting through a rotating spray unit. The present rotatable spray apparatus is particularly useful for the quenching of elongated metal workpieces, such as pipes, bars, rods, tubes and the like. Thus, for example, a pipe or rod or the like may be quenched by spray quenching as it is continuously fed along the longitudinal axis of the rotating spray unit.
It is an advantage of the present system that the rotational speed of the spray unit may be varied to meet differing process requirements, since it is not dependent on the longitudinal feed of the workpiece through the spray unit. Furthermore, the system can handle workpieces of various size and geometry and still provide uniform quenching around the workpiece surface by adjusting the rotational speed of the spray unit to the required level.
Modular construction of the present apparatus allows convenient adaptation to varying production requirements or process changes. For example, additional spray units may be added to the initial configuration or other units may be conveniently removed or relocated. Where multiple spray units are employed, the rotational speed of each unit may be individually adjusted.
Furthermore, to achieve optimum uniformity of the spray quenching, the longitudinal feed rate may be adjusted independently. In addition, the metal workpiece itself may be rotated as it travels through the rotating spray units. Typically, the elongated metal workpiece, such as pipe, rod, etc. may be moved longitudinally on rollers and by appropriate adjustment of the rollers, may be simultaneously rotated.